In a conventional so called Hi-Fi audio system, a plurality of speakers, such as a tweeter, a squeaker (midrange speaker) and a woofer, are employed for reproducing audio frequencies. These speakers are usually disposed in an enclosure and are supplied with respective signals which are obtained via a suitable frequency dividing network, such as a high-pass filter, a band-pass filter and a low-pass filter. These filters are fed with a signal which is produced in a suitable amplifier, the output impedance of which is designed to be as low as possible so that the damping factors of the speakers are large enough to perfectly reproduce the audio frequencies divided by the filters.
However, since each of the above mentioned filters comprises at least one capacitor and/or a coil, it is difficult to obtain an adequate damping factor due to the equivalent series resistance of the capacitor and/or the coil. Further, since the reactance of the capacitor is apt to undesirably vary in accordance with the variation of the frequency and the voltage applied thereto, distortion may occur by the filters, i.e the dividing network. When iron or other magnetic member is used as the core of the above mentioned coil, distortion may occur due to various reasons such as the variation of the magnetic permeability in accordance with the variation of the density of the magnetic flux that passes through the magnetic member. Moreover, since the magnetic member has hysteresis, this causes the filter to produce distortion and deteriorate the phase propagation characteristics.
From the foregoing, it will be understood that the filters used in the frequency dividing network interposed between an amplifier and the plurality of speakers, cause the speakers to deteriorate the damping characteristics thereof, while the distortion produced by the filters are directly reproduced by the speakers. In other words, frequency dividing networks have been an obstacle for the high fidelity audio reproduction.